Biotin Conjugates used with Avidin or Streptavidin for Maximum Signal Enhancement:

While the basic configuration of biotin and streptavidin results in signal amplification, the incorporation of free avidin or streptavidin with biotinylated label forms a polymeric complex that results in significantly greater sensitivity in many immunoassays. The user must determine empirically the amounts of reagents to combine for optimal signal strength. The diagram below illustrates shows this effect.

The target (T) is bound to a solid phase, i.e. ELISA plates, agarose beads, tissue sections. The binder (Ab) in this example is an antibody, but can be proteins, carbohydrates, nucleic acids or analytes. The binder is biotinylated (B) randomly at multiple sites. Unlabeled streptavidin (S) binds both to the biotinylated binder AND to the label (L) i.e. an enzyme, fluorochrome, nucleic acid, or analyte, which also contains multiple biotin moieties. This effect results in an extended polymeric structure that maximizes sensitivity in many assays.